This invention relates to a resilient seat for a butterfly valve, and more particularly to an improved method of manufacturing a resilient valve seat assembly having a flexible ring therein.
Typical resilient seats for butterfly valves are made of molded elastomeric material such as rubber. It has recently been found that an improved resilient seat is an annular seat of elastomeric material having a flexible circular band embedded therein. Such a seat assembly is disclosed in our co-pending Canadian application Ser. No. 276,542 filed Apr. 20, 1977. As described in this application, the resilient seat assembly is mounted in the body of a butterfly valve, and a circular disc is mounted within the seat assembly to seal the valve when the disc is closed.
Initially the resilient seat assembly was made by commencing with a continuous circular band or ring of flexible steel which had two holes diametrically opposed for a shaft to support the circular disc. Separate strips of material were added as stiffeners around the two holes to strengthen the band at these two areas. This construction required at least three separate pieces to be joined by welding or riveting in a somewhat complex jig.
Furthermore, when the circular band is assembled it has to be supported at the centre of a mold whilst the resilient material was inserted into the mold and allowed to harden to form the seat assembly. Supporting the band in the mold presents a number of problems, in one case the band shifted in the mold resulting in the seat assembly having the band eccentrically located and this affected the sealing of the disc on the seat. In another case, the resilient material was omitted from the outside surface of the band thus allowing the outside surface to be held in the mold during the forming step. However, it has been found that unless the band is completely embedded in the resilient material, separation occurs between the band and the material. Other methods using a mold with many parts is partially successful but the complexities of the mold and the time to assemble it cause expensive and time-consuming production.
It is, therefore, one purpose of the present invention to provide a simpler and less costly method of constructing a butterfly valve seat assembly. It is a further purpose of the present invention to provide an improved method of constructing a seat assembly with a flexible band properly embedded in resilient material.
It is another purpose of the present invention to provide an improved valve seat assembly.
In accordance with the present invention there is provided a method for making a seat assembly for a butterfly valve which comprises supporting a flexible, circular band in a fixed spatial position, positioning a mold about, but spaced from, the band while the band is supported, and molding an annular seat member from resilient material while the mold is positioned about the band to substantially embed the band within the seat member.
Furthermore, in a preferred embodiment the present invention provides the circular band being formed by overlapping the ends of two part circular, flexible band segments to form a circular band and joining the ends together.
The present invention is further directed toward a seat assembly for a butterfly valve comprising an annular, resilient seat member and a circular, flexible band embedded with the annular seat member. The circular band comprises two, part circular segments the ends of which are overlapped and joined together.
The invention will now be described in detail having reference to the accompanying drawings in which,